Epoxy resins are popular resins used in various industries as a coating composition, adhesive, electric and electronic information material, advanced composite materials, and the like due to their excellent mechanical properties. More specifically, epoxy resins are widely used in fiber reinforced composite materials comprising a reinforcing fiber such as carbon fiber, glass fiber, aramid fiber, or the like and a matrix resin. Of the polyamines, acid anhydrides, imidazoles, and the like used for the curing agent in such epoxy resin, polyamine is the most widely used agent in the application of fiber reinforced composite materials since selection of the product adequate for the application is easy due to the wide variety of polyamine products.
The method used for the preparation of the fiber reinforced composite material may be adequately selected from prepreg method, hand lay-up method, filament winding method, pultrusion method, RTM (Resin Transfer Molding) method, and the like. The fiber reinforced composite material members obtained by such method exhibit excellent strength, and such members contribute for weight reduction of aircraft parts, sports gears, automobile parts, windmill blade, and the like. In the meanwhile, demand for the weight reduction is nowadays even higher in view of environmental concern, emission control of the greenhouse gas, and the like, and further increase in the strength of the fiber reinforced composite material is awaited.
One of the most popular way of increasing the strength of the fiber reinforced composite material is increasing the strength of the reinforcing fiber, and Patent Document 1 discloses a reinforcing fiber having a high tensile strength.
Patent Document 2 discloses a prepreg and its molded article having an improved tensile strength translation rate by controlling the balance between the tensile elongation at break and fracture toughness of the matrix resin. Patent Document 3 discloses an epoxy resin composition which can be used in producing a prepreg exhibiting excellent adhesion to honeycomb core and excellent tensile strength having a rigidity modulus of the rubbery flat part of 10 MPa or less.
Patent Documents 4 to 7 disclose an epoxy resin composition prepared by using a polyamine for the curing agent. This composition was prepared as an epoxy resin composition which can be used for the process such as filament winding method, pultrusion method, or RTM method.
Patent Document 4 discloses an epoxy resin composition comprising a particular epoxy resin containing an aromatic epoxy resin having a functionality of 3 or more and a liquid aromatic amine.
Patent Document 5 discloses an epoxy resin composition comprising an epoxy resin having a functionality of 3 or more and 2 types of curing agents having different reactivity, which is used for the continuous pultrusion method. Patent Document 5 also discloses polyamines used for the curing agent.
Patent Document 6 discloses a low viscosity epoxy resin composition comprising a particular bifunctional epoxy resin and an aromatic diamine curing agent.
Patent Document 7 discloses a liquid epoxy resin composition which is curable at a low temperature comprising an aliphatic or alicyclic amine and an aromatic amine.
Patent Document 8 discloses an epoxy resin composition having at least 2 types of exothermic peaks and use of two different curing agents for the curing agent.
Patent Document 9 discloses an epoxy resin composition containing 2 types of curing agents. It has discloses that a liquid curable component can be obtained by solvation of the second curing agent with a carrier, and that it further contains the component to be cured and an epoxy component.